Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$145.67	6.833%	$155.6236	$155.62	$155.60	$155.60
Purchase #2	$63.51	10.170%	$69.969	$69.97	$69.95	$70.00
Purchase #3	$14.55	6.245%	$15.4586	$15.46	$15.45	$15.50
Purchase #4	$81.84	9.765%	$89.8317	$89.83	$89.85	$89.80
Purchase #5	$121.63	8.326%	$131.7569	$131.76	$131.75	$131.80
Purchase #6	$52.44	4.243%	$54.665	$54.67	$54.65	$54.70
Purchase #7	$34.90	11.439%	$38.8922	$38.89	$38.90	$38.90
7 purchase totals =	$514.54		$556.1970	$556.20	$556.15	$556.30